In many operations it is desirable to position and maintain a sensor element in close, but non-contacting, reliably constant proximity to a surface. For example, in high volume industrial production processes surface inspection techniques are widely utilized to assess various physical properties of painted, polished, electroplated or otherwise finished surfaces. Towards this end properties such as reflectance, light absorption, light transmission, haze and color value are frequently measured by optical sensors.
In most instances, it is desirable that these optical sensors be maintained in relatively close and repeatably constant proximity, and at a fixed angular relationship to the surface being inspected so as to allow for reliable and repeatable collection of data. It is also generally desired that the sensors be disposed in a non-contacting relationship so as to allow for high volume passage of the materials being inspected therepast, while avoiding marring or scratching of finished surfaces.
The need for precise and repeatable sensor positioning is not soley restricted to high volume industrial processes, but also arises in the taking of precision measurements. For example, analysis of photographic data frequently involves microdensitometry, photogrammetry or high resolution scanning for the digitization of images. In all of these processes, an optical sensor is disposed in close proximity to a photographic print or transparency, and moved thereacross. Obviously, in the taking of such precision measurements it is required that a precise sensor-object spacing and angular relationship be maintained and, it is further required that such precise positional relationship be repeatably obtained in subsequent measurements.
It should thus be appreciated that accurate placement of optical sensors is required in many applications ranging from high volume industrial processes to precise and constant measurement techniques, as well as will involve maintaining precise sensor-object distance as well as a constant sensor-object angle. By analogy, it will also be appreciated that precise positioning of other types of sensors such as capacitive sensors, magnetic snesors and the like will also be critical in many applications. It is further desirable, and absolutely necessary in many instances, to employ a non-contact method for maintaining the precise sensor-object positional relationship.
In those instances where mechanical complexity of the sensor device is no object and cost is no limitation, there are various technology intensive solutions to the problem of maintaining sensor position. Micropositioning apparatus of various designs are presently commercially available, however such equipment generally is expensive to purchase, and time consuming to operate. U.S. Pat. No. 3,722,996 discloses a step and repeat photo mask generating apparatus wherein precise positioning of the various optical components thereof is maintained by a hydraulic feedback loop adapted to control an air bearing. A position sensor is disposed to regulate the amount of gas provided to the bearing so as to vary the spacing between the apparatus and the subjacent surface. While this type of feedback controlled air bearing system does maintain a desired positional relationship its cost and mechanical complexity precludes its use in a high volume industrial setting.
U.S. Pat. No. 3,218,108 discloses a positioning apparatus supported by air bearings. As detailed therein, a set of air bearings is utilized solely to support and smoothly translate a work stage. The air bearings are not employed to maintain a fixed distance between the work stage and the underlying surface but rather are employed in conjunction with mechanical positioners to move the work stage in the X and Y directions.
It should be seen then that there is a need for a simple, inexpensive method and apparatus wherein sensors and the like can be rapidly precisely and repeatedly positioned relative to a subjacent surface. It is further desired that such method and apparatus will permit non-contact positioning of sensors and will be adaptable for use in a high volume, continuous process.
The present invention provides a vortex stabilized sensor system wherein an optical or other type sensor is maintained in precise spatial and angular relationship relative to a subjacent surface irrespective of dynamically changing conditions. The sensors of the present invention may be disposed to scan or inspect moving surfaces as for example in a high volume production process or may be disposed to accomplish detailed measurement of surface characteristics with a high degree of precision. The sensors of the present invention are readily adaptable for use in a large area matrix adapted to accomplish numerous, simultaneous measurements. These and other advantages of the present invention will be apparent from the drawings and description which follow.